The present invention relates to polyolefins containing one or more organic phosphites or phosphonites, or mixtures thereof, or HALS (Hindered Amine Light Stabilizer), or mixtures of the phosphites or phosphonites and HALS and optionally small quantities of one or more phenolic antioxidants, and thermoweldable fibers of the above mentioned stabilized resins that can be obtained through extrusion.
Within the definition of fibers as used herein are included also the manufactured products similar to fibers, such as fibrils, monofilaments, and raffia.
Polyolefin fibers are used widely in manufacturing thermally welded products, in particular of nonwoven textiles, through various technologies, the most important of which, like calendering and spun bonding, require that the fibers have the capability of thermowelding at temperatures lower than the melting point of the polyolefins from which they are made.
Moreover said fibers and manufactured articles obtained from them must be resistant to aging, yellowing, and to the color variations induced by gas fading and oxidizing phenomena in general.
Fibers obtained from polyolefins containing the most commonly used stabilizers, such as phenolic stabilizers, have little welding capability when they are submitted to a thermomechanical treatment carried out at a temperature lower than the melting point of the polyolefins.
Therefore, the mechanical properties of a nonwoven textile obtained by calendering the above mentioned fibers are poor.
In order to increase substantially the strength of thermowelding among the fibers, it has been suggested that bicomponent olefin fibers, i.e., constituted by two different polyolefins, such as polypropylene and polyethylene, are used, and the one with the lowest melting temperature is the one covering the surface of the fiber.
The results obtained this way are usually poor because of incompatibility between polyolefins of different chemical natures.
Italian patent application n. 22783 A/82 shows that the thermoweldability of polyolefins fibers can be improved by adding to the polyolefins of a 3,3xe2x80x2,4,4xe2x80x2-benzophenone tetracarboxylic acid di-anhydride or one of its alkyl derivative. However, fibers obtained this way have a reduced resistance to yellowing and aging.
Unexpectedly, Applicants have found that polyolefin fibers with high thermoweldability, resistant to aging, yellowing, and color variations due to xe2x80x9cgas fadingxe2x80x9d and oxidizing processes, can be obtained by starting with crystalline olefin polymers containing one or more of the following stabilizers:
a) from 0.01 to 0.5%, preferably from 0.05 to 0.15%, by weight of one or more organic phosphites or phosphonites or mixtures thereof; or
b) from 0.005 to 0.5%, preferably from 0.01 to 0.025%, by weight of one or more HALS; or
c) mixtures of (a) and (b);
and optionally one or more phenolic anti-oxidants at a concentration not exceeding 0.02% by weight.
Said olefin polymers can be in granular or nonextruded particle form, having geometrically regular form, such as flakes or spheroidal particles.
The stabilizers are incorporated during the extrusion and granulation phase of the particles, or the nonextruded particles are coated or impregnated with the stabilizers at least on the surface, preferably after the polymerization stage.
The coating or impregnation of the nonextruded particles, particularly the spheroidal particles having diameters preferably between 0.5 and 4.5 mm, can be done in a variety of ways, such as, for example, the treatment with solution or suspension of the stabilizers and an optional subsequent evaporation of the solvent or suspension medium.
Alternately, in the processes for extrusion spinning described below, the particles of polymer mixed with the above-mentioned stabilizers can be introduced directly into the extruder.
In general the additivated polyolefins used to prepare the fibers according to the present invention have a melt flow index, determined according to ASTM D 1238-L, between 0.5 and 100 g/10 minutes, more preferably between 1.5 and 35 g/10 minutes, obtained directly in polymerization or through controlled free-radical degradation or visbreaking.
In order to obtain the controlled free-radical degradation, organic peroxides are added during the granulation phase or directly in the extrusion of the fibers.
The organic phosphites that can be used as additives for polyolefins according to the present invention are preferably selected from compounds with the following general formulas: 
where R1, R2, R3, same or different, are alkyl, aryl, or arylalkyl radicals having 1-18 carbon atoms: 
where R1 and R2 have the same meaning as above;
Q is a tetravalent alkyl radical; 
where R1, R2, R3, R4, same or different, have the same meaning as indicated above for radicals R1, R2 and R3, X is a bivalent alkyl, aryl, or arylalkyl radical.
Examples or organic phosphites included in the general formula I are described in U.S. Pat. Nos. 4,187,212 and 4,290,941, which are incorporated herein by reference.
Specific examples of compounds included in general formulas I, II, III are: tris(2,4-di-ter-butylphenyl)phosphite sold by CIBA GEIGY under the Irgafos 168 trademark; distearyl pentaerythritol diphosphite sold by BORG-WARNER CHEMICAL under the Weston 618 trademark; 4,4xe2x80x2-butylidene-bis(3-methyl-6-ter-butylphenyl-di-tridecyl)phosphite sold by ADEKA ARGUS CHEMICAL under the Mark P trademark; tris(monononylphenyl)phosphite; bis(2,4-di-ter-butyl)pentaerythritol diphosphite, sold by BORG-WARNER CHEMICAL under the Ultranox 626 trademark.
The organic phosphonites that can be used as additives according to the present invention are preferably selected from the compounds of general formula: 
where R1, R2, R3, same or different, are alkyl, aryl, or arylalkyl radicals having 1-18 carbon atoms, or R3 is the radical having the formula: 
where R4 and R5, same or different, have the same meaning as indicated for the R1 and R2 radicals, and X is a bivalent alkyl, aryl, or arylalkyl radical.
Examples of organic phosphonites included in general formula IV, which can conveniently be used according to the present invention, are described in GB patent No. 1,372,528. which is incorporated herein for reference.
A preferred example of compounds comprised in general formula IV is the stabilizer compositions, the main compound of which is tetrakis(2,4-di-ter-butylphenyl)4,4xe2x80x2-diphenylene diphosphonate sold by Sandoz under the Sandostab P-EPQ trademark.
The organic phosphites and phosphonites are generally used to inhibit degradation and oxidation of polyolefins in the molten state (process stabilizers), and therefore, according to known state of the art, require the addition of high quantities of phenolic stabilizers to obtain a complete stabilization.
The HALS, which according to the present invention are also used as polyolefin stabilizers, are amine compounds with steric hindrance of the amine function, which are generally used as stabilizers for polyolefins in the solid state against oxidation induced by light.
In this case as well, according to known state of the art, the addition of a high quantity of phenolic stabilizers is necessary for a satisfactory stabilization of polyolefin manufactured articles.
The HALS used according to the present invention are monomeric or oligomeric compounds containing, in the molecule, one or more substituted piperidyl groups having the following general formula: 
where the R1 radicals, same or different, are C1-C4 alkyl radicals, or tetramethylpiperidine radicals, or the alkyl radicals form, together with the piperidyl carbon atom to which they are bonded a C5-C9 cycloalkyl radical; R2 radicals, same or different, are hydrogen, C1-C18 alkyl radicals, C7-C18 arylalkyl radicals, or the alkyl radical form, together with the piperidyl carbon atoms to which they are bonded a C5-C10 cycloalkyl radical; R3 radicals, same or different, are hydrogen, C1-C18 alkyl radicals or C7-C18 arylalkyl radicals; the R4 radical is hydrogen, a C1-C8 alkyl radical, or a benzyl radical; Z is hydrogen, a C1-C18 alkyl, C1-C12 alkylene, C3-C12 alkenyl, C3-C5 alkynyl, C7-C18 arylalkyl, C2-C4 acyl, C2-C18 alkanoyl, C3-C18 alkoxyalkyl, C3-C18 alkenoyl, oxyl, cyanomethyl, xylylenyl radical, or a radical having a valence from 1 to 4 and containing from 1 to 4 hydroxyl groups and, optionally containing ether, ester, or heterocyclic groups, all valences of said radical being bonded to the nitrogen of piperidyl rings, or a bivalent radical containing one or more ester or amide group, or a 
radical where R5 and R6 are hydrocarbon radicals.
Preferably Z is a C1-C12 alkyl, a C3-C8 alkenyl, C7-C11 aralkyl radical, or a bivalent radical containing one or more ester groups, wherein the valences of said radicals are bonded to the nitrogen of the piperidyl rings.
Specific examples of preferred HALS according to the present invention are compounds having the following formula: 
where n is from 2 to 20. A compound of this type is sold by CIBA-GEIGY with the Chimassorb 944 trademark. 
sold by CIBA-GEIGY under the Chimassorb 905 trademark, where R is: 
sold by CIBA-GEIGY under the Tinuvin 770 trademark; 
sold by CIBA-GEIGY under the Tinuvin 292 trademark; 
where n is from 2 to 20, such as the compound sold by CIBA-GEIGY under the Tinuvin 622 trademark; 
sold by CIBA-GEIGY under the Tinuvin 144 trademark; 
where n is from 2 to 20, such as the compound sold by CIBA-GEIGY under the Spinuvex A36 trademark; or 
where n is from 2 to 20, such as the compound sold by AMERICAN CYANAMID under the Cyasorb UV 3346 trademark.
As previously stated, in addition to the above-mentioned additives optionally, one or more phenolic antioxidants (sterically hindered phenols) can be used in concentration not greater than 0.02% by weight.
Examples of preferred phenolic antioxidants are: tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-s-triazine-2,4,6-(1H, 3H, 5H)trione, sold by AMERICAN CYANAMID under the Cyanox 1790 trademark; calcium bi[monoethyl(3,5-di-ter-butyl-4-hydroxybenzyl)phosphonate]; 1,3,5-tris (3,5-di-ter-butyl-4-hydroxybenzyl)-s-triazine-2,4,6(1H,3H,5H) trione; 1,3,5-trimethyl-2,4,6-tris(3,5-di-ter-butyl-4-hydroxybenzyl)benzene; pentaerythritol-tetrakis[3(3,5-di-ter-butyl-4-hydroxyphenyl)propionate], sold by CIBA-GEIGY under the following trademarks: Irganox 1425, Irganox 3114; Irganox 1330 and Irganox 1010; 2,6-dimethyl-3-hydroxy-4-ter-butyl benzyl abietate.
The additives commonly used to stabilize polyolefins, particularly Ca, mg, Zn stearates, can also be used in the preparation of the fibers according to the invention.
The polyolefins which can be used in the present invention comprise crystalline polymers or copolymers, or their mixtures, of olefins of the Rxe2x80x94CHxe2x80x94CH2 formula where R is a hydrogen or a C1-C6 alkyl radical.
Particularly used are:
1) isotactic or predominantly isotactic polypropylene;
2) high density, linear low density and low density polyethylene;
3) crystalline copolymers of propylene with ethylene or with C4-C8 linear or branched alpha-olefins, such as, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, where the total comonomer content varies from 0.05% to 20% by weight;
4) heterophasic polymers comprising (A) a homopolymer of propylene or one of the copolymers of (3), above and (B) an ethylene-propylene or ethylene-propylene-diene rubber polymer. Said heterophasic polymers being prepared according to known methods via mixing in the melted state of the above-mentioned components, or sequential polymerization in the same reactor or series of reactors, wherein (B) is present in amount from 5% to 80% by weight, and (A) in an amount from 20% to 80% by weight;
5) syndiotactic polypropylene and its copolymers and heterophasic copolymers thereof as described in (3) and (4) above.
Preferred are isotactic or predominantly isotactic polypropylene, and crystalline propylene-ethylene copolymers having a propylene content of 75%-98%.
In order to obtain thermoweldable polyolefin fibers according to the present invention, any spinning process and apparatus for melt extrusion known in the field may be used.
The present invention comprises, therefore, also the thermoweldable polyolefin fibers-containing the stabilizers in the above-mentioned quantities.
For the preparation of the fibers of the invention it is preferable to use extruders with spinnerable holes having a length/diameter ratio greater than 2.
The operation can occur at a spinning temperature between 260xc2x0 C. and 300xc2x0 C., and at a spinning velocity between 0.1 and 0.8 g/min per hole.
During the spinning it is possible to introduce into fibers other additives such as pigments, opacizers, fillers, etc.
The fibers obtained by extrusion are eventually submitted to stretching with stretching ratios generally between 1:1.1 and 1:8 and at temperatures between 80xc2x0 C. and 150xc2x0 C., preferably between 100xc2x0 and 130xc2x0 C., using stretching apparatus heated, i.e., with hot air, vapor, or heating plates.
The melt flow index of the fibers obtained in this manner is usually higher with respect to the values of the original polyolefins because of the spinning treatment.
Indicatively, one can obtain melt flow index values for the fibers between 4 and 150 g/10 minutes.
The fibers obtained according to the above-mentioned methods can be mono- or multifilament, and may be used for the preparation of staples or thermally adhered products, especially of nonwoven textiles.
Optionally, before the transformation to finished manufactured articles, the fibers can be submitted to refinishing treatments such as crimp, thermofixing, etc.
As previously stated, the nonwoven textiles may be prepared with a variety of known technologies, such as the calendering of staple fibers and the spun bonding, operating preferably at a temperature of 10-20xc2x0 C. lower than the melt temperature of the polyolefins from which the fibers are made.
The products have high mechanical properties, because of the mechanical resistance of the thermowelding that can be obtained with the fibers of the present invention.
The above-mentioned fibers, in fact, are characterized by a high thermowelding strength, determined according to the method described in the examples. Preferably this parameter varies from 2 to 5 N.
Moreover, the manufactured articles derived from the fibers of the present invention show satisfactory resistance to aging and color changes.
Following are some examples which are given to illustrate but not to limit the invention.
Thermowelding Strength
Usually, in order to evaluate the thermowelding ability of the fibers it is customary to produce a nonwoven via calendering under special conditions, and measure the stress necessary to tear the nonwoven in a direction transverse to the calendering one, operating according to ASTM 1682.
The stress value determined in this manner is considered a measure of the ability of the fiber to thermoweld.
The result obtained, however, is influenced substantially by the finishing characteristics of the fibers (crimp, finish, thermofixing, etc.) and the condition of preparation of the card veil fed to the calender.
In order to prevent these inconveniences and obtain a more direct evaluation of the thermowelding characteristics of the fibers, a method has been devised which is schematically described below.
Some samples were prepared starting with a rove of 400 tex (ASTM D 1577-7) and 0.4 m long, made up of continuous fibers.
After having twisted said rove eighty times, the two extremities were joined, obtaining a manufactured article where the two halves of the rove were twisted around each other as in a rope.
The two twisted roves were thermowelded at a temperature of about 15xc2x0 C. lower than the melting point of the polyolefin from which the fibers are made, operating for a predetermined period of time with a thermowelder of the type commonly used in laboratories for the study of thermoplastic films.
The average force required to detach the two roves of each sample at the thermowelded point was measured with a dynamometer.
The result, expressed in N, was obtained by averaging out at least 8 measurements, and it expressed the thermowelding strength of the fibers.
In the following examples a Sentinel model 12-12 AS thermowelder was used, operating with thermowelding periods of 1 second and a thermowelding pressure of about 2.85 Kg/cm2.
Color Changes
The IXSO/TC38/SC1 norm was used at 60xc2x0 C. and at 130xc2x0 C. to measure the resistance of fibers to colorations induced by gas fading.
The resistance to colorations induced by oxidation phenomena was measured by keeping the fibers in an oven at 90xc2x0 C. for 2 days, and the coloration was evaluated based on the gray scale, as described in the above-mentioned norm.
Resistance to Artificial Aging
This property was evaluated by submitting the fibers to accelerated aging in a ventilated oven at 110xc2x0 C., according to ASTM D 3045-74.
The time (in days) necessary to reach total decay of the mechanical properties (embrittlement) was determined.